The present invention relates to a process for processing continuous fibers into finer continuous fibers (this process is called "splitting" herein, and the finer continuous fibers are called "split fibers") and arranging them to form a sheet-like material, and an apparatus for the production of such sheet-like material comprising the split fibers.
Methods for finely splitting continuous fibers have heretofore been extensively studied. Fiber-splitting methods for synthetic fibers produced by the molten spinning process which are well known in the art include methods in which static electricity is applied and splitting is achieved by the action of the electrical repulsion force, and in which splitting is achieved by blowing an air stream onto the continuous fibers. These methods are now in widespread use.
If carbon fibers could be effectively split, one would be able to easily produce a sheet-like material in which split fibers are properly arranged in one direction. It is, however, very difficult to split continuous carbon fibers by the conventional methods described above since the carbon fibers are readily damaged by only slight friction, unlike other synthetic fibers, resulting in the formation of fluff; and since they are electrically conductive.
Since carbon fibers exhibit good affinity with liquids such as water and alcohols, if fiber-splitting could be conducted by the utilization of such liquids, a very useful method would result.
A method of splitting continuous fibers and forming a sheet-like material by the utilization of a liquid stream, e.g., water, is known, as described in, for example, Japanese Patent Application (OPI) No. 121568/75, in which the equipment illustrated in FIG. 1 is used.
Referring to FIG. 1, a plurality of continuous fiber bundles 18 are introduced into a liquid tank 1 at a fixed rate by means of a pair of feed rollers 19 and, thereafter, are introduced into a liquid stream through a slit-like exit 5 by a suction action and fed to an inclined splitting unit 8, where the fibers are split in the lengthwise direction. In this method, however, the liquid stream in the inclined splitting unit 8 can freely extend its width toward the lower end of the unit 8 and, therefore, a plurality of continuous fiber bundles fed as a combined material of monofilaments partially overlap one another. This partial overlapping causes a difference in resistance in the width direction of the liquid diffusion-flowing in the inclined splitting unit 8, thereby producing an unevenness in the arrangement of the split fibers. Thus there can be obtained only an uneven sheet-like material as illustrated in FIG. 2, in which the split fibers are not uniformly arranged or disposed in the width direction of the sheet-like material. Furthermore, the twist that the continuous fiber bundle per se possesses makes it impossible to achieve splitting according to the above method. The reasons for this are that (1) it is difficult to stabilize the liquid stream containing intertwisted or twisted fiber bundles, and (2) in feeding the continuous fiber bundles to the liquid stream, air is entrained in the liquid stream, making it impossible to achieve uniform splitting continuously.